Tag and tagging system

ABSTRACT

A tag comprising a plastic container having at least one particle therein. The or each particle may be formed from metal or metal coated and/or fabricated from a plurality of different metals. A receiver unit adapted to detect RF pulses arising as a result of the Triboelectric effect of the particles enables detection of a tag.

This invention relates to a tag and tagging system.

There are many examples of tags. In recent years electronic tags have been developed which store data and from which data can be retrieved by way of radio frequency (RF) or capacitive interrogation. These so-called smart tags are sophisticated often having their own energy supply or a means for deriving energy from an interrogator usually by way of inductive or capacitive coupling. Such smart tags are extremely effective at performing their intended purpose, but they are complex and expensive.

According to the first aspect of the invention there is provided a tag comprising: a container, in which there is at least one particle, arranged to be displaced with respect to the container so that a radio frequency (RF) signature is emitted; said RF signature being capable of identifying the tag

The generation of electric charge by contact between two surfaces is known as the Triboelectric effect. The static charge is not caused directly by friction but by adhesion between two surfaces at molecular level. Surfaces stick together because chemical bonds form. When surfaces in contact separate these bonds rupture and any asymmetrical bonds tend to leave a charger imbalance due to an interchange of electrons between the surfaces.

The inventors have determined that use can be made of this effect to provide a tagging system, which is very sensitive to movement.

The tag described herein allows for a very low cost and simple means to apply tagging. Specifically it provides a cheap and simple means to generate a tagging signal. The invention will now be described in more detail.

In general the invention takes the form of a number of metal particles placed in a plastic container, such as a synthetic plastics bag, envelope or other capsule for example. When displaced with respect to one another very short pulses of electromagnetic energy at radio frequencies are produced. The pulse width is very small and is typically less than a nanosecond (ins) in duration. Typically the amplitude of the pulse (spike) is of the order of a few hundred Milliwatts ERP.

Pulses are generated for example by having a static charge build up on individual particles as they move over a synthetic plastic surfaces. Because the movement in different parts of the bag varies, there is a significant difference between electric charge on individual particles. This difference abruptly reduces to zero when they touch. This rapid voltage step generates electromagnetic pulses.

A passive tag may be provided for example by the use of a miniature synthetic plastics capsule or pill containing metal particles. Pulses generated can be detected using a wideband receiver with a bandwidth in the order of 1 GHz.

Preferably the receiver has a detector which is capable of detecting pulse signals with a rise time of around 1 nanosecond.

Various applications of such tags are envisaged. These include applications in goods or other articles. In a system using the tag for example, an alarm is triggered in the event that articles are removed from a shop without authorisation (ie., without removing the tag). Other applications may include tagging of valuable articles; and tagging of humans and tagging of animals.

There are a number of different forms or materials from which the tags may be fabricated. For example, they may be manufactured as a blister pack with each tag being of the order of a few millimetres in the form of a cube. The container is ideally formed from a synthetic plastics material and the particles include a conductive material such as metal particle. Although metal particles are preferred the invention is not limited to this but other conducting materials such as carbon may also be used.

The tags may also contain particles of a variety of different materials conductive and non-conductive materials of differing particle size. In this way tags are capable of providing a different pulse signature which is individual to each tag and thus detection of these would differentiate one tag from another.

This provides tags suitable for verification purposes. Thus, for example, an envelope or container having a number of particles, the nature or characteristics of pulses emitted may be related to the number of particles.

Because pulses generated are of very narrow width (duration) it is possible to locate the tag accurately by measuring the time of arrival of the pulses using two or more suitably spaced detectors.

An embodiment will now be described with reference to the FIGURE in which there is shown a tag.

In one particular preferred embodiment of the invention, shown in FIG. 1, a tag includes a container 12 formed from a synthetic plastics tube 11 within which there is a metal particle in the form of a sphere 14. The tube 11 has a series of metallic strips 16, 18 and 20 in the form of rings disposed on the surface of the container 12. As the sphere 14 rolls along the tube 11 a series of RF pulses are emitted. The quantity and width of the strips determine the pulse train. Such an embodiment allows for differentiation of one tag from another tag.

The invention has been described by way of an example only and variation may be made to it without departing from the scope of the invention. 

1. A tag comprising a container in which there is at least one particle, arranged to be displaced with respect to the container so that a radio frequency (RF) signature is emitted, said RF signature being capable of identifying the tag.
 2. A tag as claimed in claim 1 having a plurality of particles.
 3. A tag as claimed in claim 1, wherein the or each particle is/are metal or metal coated.
 4. A tag as claimed in claim 3 wherein the metal or metal coated particle(s) are fabricated from a plurality of different metals.
 5. A tag according to claim 1, having two or more metallic strips disposed on the surface of the container arranged to detect displacement of the or each particle.
 6. A tag according to claim 5 wherein the relative location and/or dimension and/or number of strips on a tag is different, thereby providing a different RF signature upon displacement of the or each particle.
 7. A tagging system comprising a tag as claimed in claim 1, and a receiver unit adapted to detect RF signals.
 8. A tagging system as claimed in claim 7 wherein the receiver is a wideband receiver having a bandwidth of at least 0.5 GHz.
 9. A tagging system as claimed in claim 7 wherein the receiver is a wideband receiver having a bandwidth of at least 1 GHz.
 10. A tagging system as claimed in claim 7, having means to locate the tag.
 11. A tagging system as claimed in claim 10 wherein the means to locate the tag includes first and second receivers which are operative to locate a tag based upon the time of arrival of a signal at each receiver.
 12. A method of tagging an object using a tag according to claim 1 and detecting RF signals.
 13. A method as claimed in claim 12 wherein different tags are distinguished by virtue of the number and type of particles in each tag. 